In many filter constructions, assemblies are provided which include a removable canister which houses the filter element. Often in industrial filtering applications, pressure within the filter can reach 2,000 p.s.i., or more. To protect against leakage at the area joining the canister to the filter body or head, the canister must be tightly and securely held to the filter head. A common solution to the problem of providing a tight and secure assembly which prevents leakage is to provide compression seals or other gasket-type sealing members between the canister and the filter head.
For proper operation of the filter, it is necessary that a schedule for periodic maintenance be followed. To maintain the integrity of the seals through multiple disassemblies for the purpose of replacing the filter element, different coupling mechanisms between the filter head and canister have been suggested. One such coupling is shown in my U.S. Pat. No. 4,316,801 which discloses a jackscrew connection between the filter head and canister. Wear of the seal between the filter head and canister is minimized since the canister does not rotate relative to the filter head as it is removed or replaced. Instead, the canister is jacked on and off the filter head by the jackscrew which is rotatably mounted on the canister.
Unfortunately, even with the arrangement disclosed in my earlier patent, many combined factors can contribute to a condition in which the canister is difficult to remove from the filter head. One factor is the tight engagement between the canister and filter head which is required to prevent leaks at high pressure operation. Also, the filter is often exposed to environmental conditions resulting in corrosive build-up at the mating joint of the canister and filter head. High internal fluid pressure is another factor which may contribute to difficult canister removal by causing expansion of the sealing members which results in an even tighter engagement between the filter head and the canister. Finally, in some applications, the filter may be exposed to thermal cycling which expands and contracts filter parts into an even tighter engagement than originally achieved.
Because of this difficulty, periodic maintenance has sometimes been ignored. As a result, the filter becomes too clogged to pass fluid, which causes a safety pressure relief valve to open and allow the fluid to bypass the filter element. While the fluid system continues to function, the fluid no longer is cleaned of the contaminants. As a consequence, the useful life of the fluid system is shortened and the system integrity compromised.
In an attempt to free up a seemingly frozen connection between the canister and the filter element, ad hoc procedures have been used such as vibrating the joining area between the filter head and canister by firmly tapping the filter assembly. Repeated use of such a procedure can damage the structural integrity of the filter assembly. In addition, special tools, such as strap wrenches, are typically required to tighten or loosen a filter canister, or a jackscrew such as is disclosed in my earlier patent. The difficulty and need for special tools to loosen the canister creates a condition which discourages periodic disassembly of the filter for replacement of the filter element.